/*
 * Base64.java
 *
 * Created on April 15, 2007, 4:24 AM
 *
 * To change this template, choose Tools | Template Manager
 * and open the template in the editor.
 */

// Copyright (C) 2001 Stefan Haustein, Oberhausen (Rhld.), Germany
//
// Contributors: 
//
// License: LGPL
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public License
// as published by the Free Software Foundation; either version 2.1 of
// the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
// USA
package com.yuven.baselib.utils.security;

import java.io.ByteArrayOutputStream;

/**
 * Converter to and from base 64.
 *
 * @author Stefan Haustein
 */
public final class Base64 {

    static final char[] CHAR_TAB = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
            .toCharArray();

    /**
     * Create a base64 encoded string.
     *
     * @param data
     * @return encoded
     */
    public static String encode(byte[] data) {
        return encode(data, 0, data.length, null).toString();
    }

    /**
     * Encodes the part of the given byte array denoted by start and len to the
     * Base64 format. The encoded data is appended to the given StringBuffer. If
     * no StringBuffer is given, a new one is created automatically. The
     * StringBuilder is the return value of this method.
     *
     * @param data
     * @param start
     * @param len
     * @param buf
     * @return Encoded string
     */
    public static StringBuilder encode(byte[] data, int start, int len,
                                       StringBuilder buf) {

        if (buf == null) {
            buf = new StringBuilder(data.length * 3 / 2);
        }

        int end = len - 3;
        int i = start;
        int n = 0;

        while (i <= end) {
            int d = (((data[i]) & 0x0ff) << 16)
                    | (((data[i + 1]) & 0x0ff) << 8) | ((data[i + 2]) & 0x0ff);

            buf.append(CHAR_TAB[(d >> 18) & 63]);
            buf.append(CHAR_TAB[(d >> 12) & 63]);
            buf.append(CHAR_TAB[(d >> 6) & 63]);
            buf.append(CHAR_TAB[d & 63]);

            i += 3;
        }

        if (i == start + len - 2) {
            int d = (((data[i]) & 0x0ff) << 16) | (((data[i + 1]) & 255) << 8);

            buf.append(CHAR_TAB[(d >> 18) & 63]);
            buf.append(CHAR_TAB[(d >> 12) & 63]);
            buf.append(CHAR_TAB[(d >> 6) & 63]);
            buf.append("=");
        } else if (i == start + len - 1) {
            int d = ((data[i]) & 0x0ff) << 16;

            buf.append(CHAR_TAB[(d >> 18) & 63]);
            buf.append(CHAR_TAB[(d >> 12) & 63]);
            buf.append("==");
        }

        return buf;
    }

    static int decode(char c) {
        if (c >= 'A' && c <= 'Z') {
            return (c) - 65;
        } else if (c >= 'a' && c <= 'z') {
            return (c) - 97 + 26;
        } else if (c >= '0' && c <= '9') {
            return (c) - 48 + 26 + 26;
        } else {
            switch (c) {
                case '+':
                    return 62;
                case '/':
                    return 63;
                case '=':
                    return 0;
                default:
                    String e = new StringBuilder().append("错误的数据格式引起decode出错: ").append(c).toString();
                    throw new RuntimeException();
            }
        }
    }

    /**
     * Decodes the given Base64 encoded String to a new byte array. The byte
     * array holding the decoded data is returned.
     *
     * @param s
     * @return The real thingi
     */
    private static ByteArrayOutputStream decodeToStream(String s) {
        int i = 0;
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        int len = s.length();

        while (true) {
            while (i < len && s.charAt(i) <= ' ') {
                i++;
            }

            if (i == len) {
                break;
            }

            char ch0 = s.charAt(i);
            char ch1 = s.charAt(i + 1);
            char ch2 = s.charAt(i + 2);
            char ch3 = s.charAt(i + 3);
            int tri = (decode(ch0) << 18) + (decode(ch1) << 12)
                    + (decode(ch2) << 6) + (decode(ch3));

            bos.write((tri >> 16) & 255);
            if (s.charAt(i + 2) == '=') {
                break;
            }
            bos.write((tri >> 8) & 255);
            if (s.charAt(i + 3) == '=') {
                break;
            }
            bos.write(tri & 255);

            i += 4;
        }
        return bos;
    }

    public static byte[] decodeToBytes(String s) {
        return (s == null) ? null : decodeToStream(s).toByteArray();
    }

    public static String decodeToString(String s) {
        return (s == null) ? null : decodeToStream(s).toString();
    }
}
